A large number of so-called “direct engraving CTP methods”, in which a relief-forming layer is directly engraved by means of a laser are proposed. In the method, a laser light is directly irradiated to a flexographic printing plate precursor to cause thermal decomposition and volatilization by photothermal conversion, thereby forming a concave part. Differing from a relief formation using an original image film, the direct engraving CTP method can control freely relief shapes. Consequently, when such image as an outline character is to be formed, it is also possible to engrave that region deeper than other regions, or, in the case of a fine halftone dot image, it is possible, taking into consideration resistance to printing pressure, to engrave while adding a shoulder. With regard to the laser for use in the method, a high-power carbon dioxide laser is generally used. In the case of the carbon dioxide laser, all organic compounds can absorb the irradiation energy and convert it into heat. On the other hand, inexpensive and small-sized semiconductor lasers have been developed, wherein, since they emit visible lights and near infrared lights, it is necessary to absorb the laser light and convert it into heat.
As a conventional resin composition for laser engraving, those described in International Patent Application WO 2006/051863, JP-A-2007-148322 (JP-A denotes a Japanese unexamined patent application publication), JP-A-2005-534525, JP-A-2010-69763 or JP-A-2007-520379 are known. As a conventional resin composition for solvent development, those described in JP-A-2010-222591 are known.